Conventionally, it is common that an interior material for a vehicle includes an intermediate layer made of glass fibers as a reinforcing material. Recently, it has been proposed that the intermediate layer of the interior material structure be made of carbon fibers. See, for example, JP63-158449U, JP2003-260718A, or JP2003-305789A.
However, such a proposed interior material structure including the carbon fibers faces a new problem in that vehicle electric noises are distributed through a conductive portion of the interior material since the carbon fibers are conductive. In this context, the vehicle electric noises include, for example, ignition noise generated from an internal combustion engine, noises from electric motors, actuators, and the like for electric power steering, an air conditioner, electronic braking force control, and headlamp exposure area control, or any other electric noises in general which may be generated in the vehicle.
During such distribution of the vehicle electric noises, a glass antenna placed on a rear window becomes controversial. This is conceptually illustrated in FIG. 1A. When the vehicle electric noises distributed through a roof harness 101 and reaching a roof portion of a vehicle 100 induce and distribute electric noises in the conductive portion of the interior material, such induced electric noises may radiate to a glass antenna 102 at a rear end of the roof and affect the performance of the antenna.
This becomes more apparent as the interior material on the roof portion is provided closer to the rear window. According to the inventors' experimental knowledge, in terms of a frequency band, a glass antenna for AM radio is strongly affected, among others. However, it is rather difficult to say that other glass antennas such as ones for FM radio or TV are not affected at all.